1. Field of the Invention
The present invention relates to a phosphate-based dielectric ceramic composition which has dielectric characteristics suitable to use as a substrate material for electronic components having internal conductors such as resonators, multilayer ceramic capacitors, dielectric filters, antennas, dielectric waveguides for microwave integrating circuit (MIC) in the microwave region, and a method for manufacturing a dielectric substrate using the ceramic composition. Since the dielectric ceramic composition has excellent dielectric characteristics, e.g., a low dielectric loss, a low dielectric constant and excellent temperature stability, and can be sintered at low temperature in combination with an additive, it can be simultaneously calcined together with a metal electrode such as silver, copper or silver/palladium electrode.
2. Description of the Related Art
With high-speed information transmission and recent development of mobile communication techniques, demand for light, compact and high-integrated circuits has been increasing. In addition, as the number of signals transmitted increases, studies on the use of high frequencies ranging from a few GHz and higher are being actively undertaken. There is thus a strong demand for dielectric compositions used as materials for electronic components and substrates in the high-frequency bands.
Generally, as the dielectric constant of a dielectric is low, the transmission speed of signals inside the dielectric is high. Accordingly, it is preferred that electronic components used in the high-frequency bands have a low dielectric constant. In order to improve the selectiveness of the signal transmission, dielectrics having a low dielectric loss, i.e. high Q-factor, and excellent temperature stability are required.
As electrically conductive materials used as internal conductors and electrodes of packaging substrates, inexpensive metals such as Ag and Cu are advantageously used because they have a low specific resistance, resulting in less loss and heat. However, since these metal electrodes have a melting point of lower than 1,000° C., dielectric compositions used in combination with substrates must be calcined at a temperature of not lower than 1,000° C. for simultaneous calcination.
A representative example of ceramic compositions which can be calcined at low temperature among conventional substrate materials is glass ceramics. Since the glass ceramics is manufactured by incorporating a large amount of a glass component into a ceramic such as alumina, it can be calcined even at low temperature by glass softening. In addition, various combinations of glass with a ceramic can improve the physical properties of glass ceramics.
Japanese Patent Laid-Open No. 10-297960 discloses a ceramic composition having a low dielectric constant and a low dielectric loss which comprises Zn2SiO4 and SiO2 as a ceramic and SiO2—Li2O—ZnO glass. According to the ceramic composition, calcination at 800˜1,000° C. is possible.
Although the glass ceramics is advantageous in terms of its low dielectric constant resulting from the presence of a large amount of glass, it has disadvantages of a considerably reduced Q-factor and a high dielectric loss in the high-frequency bands. Additionally, the glass ceramics has poor temperature stability because the resonance frequency temperature coefficient cannot be stably controlled.